424 THE RABBIT. PHYLUM CHORDATA 



cervical, chest or thoracic, loin or lumbar, hip or sacral, and 

 tail or caudal regions. In the cervical region there are in all 

 mammals seven vertebrae, which may be recognised by the fact 

 that apparently each of the transverse processes is pierced by 

 an opening (its foramen) : there is thus formed on each side a 

 vertebrarterial canal, through which pass the vertebral artery and 

 vein. This is due to the fusion with the vertebrae of short cervical 

 ribs in such a way as to constitute a compound ' transverse 

 process ' which encloses a space. The first vertebra, known as 

 the atlas, is ring-shaped, with a very large vertebral foramen and 

 no centrum. The ring is divided by a ligament into an upper 

 part, through which the spinal cord passes, and a lower part, 

 into which fits a peg, the odontoid process, projecting forward 

 from the centrum of the second vertebra. This peg represents 

 the centrum of the atlas removed from it and fused with the 

 vertebra behind. The transverse processes of the atlas are very 

 broad, and the front side of the vertebra has two very large 

 articular surfaces for the occipital condyles of the skull. The 

 second vertebra is known as the axis. It has a long, crest-like 

 neural spine and bears the odontoid process. The remaining 

 cervical vertebrae are short and broad, with low neural spines, 

 but that of the seventh is longer than the others. The thoracic 

 region contains twelve or thirteen vertebrae, which are character- 

 ised by bearing movably articulated ribs. The neural spines are 

 tall, the transverse processes short and stout, and each, in the first 

 nine vertebrae, provided on the under side with a facet or * costal 

 pit ' for articulation with the tubercle of a rib, presently to be 

 described. The front end of the centrum (in the first nine the hinder 

 end also) bears on each side a facet for the head of the rib. The 

 hinder vertebrae of this set gradually become more like those of 

 the lumbar region. These are usually seven in number. They are 

 characterised by their large size and the great development of 

 their processes, the prezygapophysis being borne upon the inner 

 side of a large metapophysis and the hinder intervertebral notch 

 being overhung by a small anapophysis. In the first two the 

 centrum bears a median ventral hypapophysis. The lumbar 

 vertebrae have no ribs. The sacral vertebrae are those to which the 

 hip girdle is attached ; there is usually only one, but sometimes 

 two are found. These vertebrae are large and bear at the sides 

 a pair of wing-like expansions, w^hich support the hip girdle 

 and are probably ribs fused with the vertebra. A certain number 



